RFR: 8272343: Remove MetaspaceClosure::FLAG_MASK

[Ioi Lam]

On Wed, 25 Aug 2021 21:32:59 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

>> Please review this simple fix. `MetaspaceClosure::FLAG_MASK` is no longer needed after https://bugs.openjdk.java.net/browse/JDK-8272107
>
> The cleanup looks good.

Thanks @calvinccheung and @yminqi for the review.

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PR: https://git.openjdk.java.net/jdk/pull/5245